The field of the invention is that of silicon semiconductor processing, in particular forming vertical CMOS transistors.
In the constant drive to save space, advanced CMOS processing techniques now include CMOS transistors that are oriented vertically. When a trench is etched into a silicon substrate, a transistor formed in the trench with a vertical orientation will have its gate exposed to two different crystal orientations, and it is known in the art that oxide grows at distinctly different rates on the  less than 100 greater than  and  less than 110 greater than  crystal planes. The difference in growth rates on these planes typically ranges between 40% and 100%.
It has been reported in U.S. Pat. No. 6,358,867 that a growth ratio of 0.9 for the  less than 100 greater than  and  less than 110 greater than  planes has been achieved using a low pressure mixture of hydrogen and oxygen.
This improvement still falls short of the ideal goal of equal growth rates, which will result in still better quality transistors and other structures formed on complex multi-crystal orientation surfaces.
The art still needs an improved method of growing high-quality oxide on complex surfaces of silicon having at least two crystallographic orientations.
The invention relates to a method of growing oxide on a complex surface that achieves a ratio of growth rates of 99%.
A feature of the invention is that a small ratio of nitride thickness to final oxide thickness is preferred.
A feature of the invention is the use of a prebake step in a nitrogen-containing ambient.
Another feature of the invention is nitride deposition with the use of an ammonia ambient at an elevated temperature.
Another feature of the invention is a prebake temperature range of between 500xc2x0 C. and 1100xc2x0 C.